1. Field of the Invention
The invention relates to an ultraviolet-ozone oxidation system and method, and more particularly, the invention relates to a cleaning-stripping apparatus using a combination of ultraviolet radiation and ozone.
2. Brief Description of the Related Art
Ultraviolet-ozone cleaning-stripping systems have been used as an effective method to remove a variety of contaminants from the surfaces of semi-conductors as well as many other surfaces. Ultraviolet-ozone cleaning is a simple to use and inexpensive process for removing contaminants from semi-conductors. One of the uses of ultraviolet-ozone cleaning is to strip away organic layers, such as photo resist layers, or other organic contamination from a semi-conductor work piece during the manufacture of silicon-based electronic devices.
It is generally thought that the combination of ultraviolet (UV) light and ozone destroys organic compounds by photosensitized oxidation. The organic molecules are excited, dissociated, or depolymerized by short-wavelength UV light, such as the light emitted by a low-pressure mercury lamp in a quartz envelope. These excited molecules are particularly likely to undergo oxidation by atomic oxygen, ozone, or other minor oxidants. One primary reaction thought to occur when ozone and oxygen molecules are exposed to UV radiation from the mercury lamp is the conversion of oxygen to ozone. At elevated temperatures, a second reaction occurs in which ozone thermally decomposes in the gas phase forming atomic and molecular oxygen.
An auxiliary ozone generator is often added to a UV-ozone cleaning system to further increase the concentration of oxidants and thereby shorten the process time. It has also been shown that an elevated temperature in the UV-ozone oxidation system accelerates the rate of oxidation of organic matter. For example, with an ozone/oxygen flow rate of 0.5 liters per minute and an ozone concentration of 6.4 grams per cubic meter, the rate of oxidation of a photo resist at 150xc2x0 C. was only 54 Angstroms per minute, while at 300xc2x0 C. the rate of oxidation increased to 596 Angstroms per minute, i.e., ten times faster.
The UV-ozone oxidation equipment used to carry out stripping and cleaning generally includes a base or sample stage upon which a work piece is placed inside a reaction chamber. The reaction chamber is provided with a source of ultraviolet light focused on the work piece and an ozone source capable of delivering a mixture of ozone and oxygen to the reaction chamber over the work piece. However, current UV-ozone oxidation systems lack uniformity of oxidation across the entire surface of the work piece and lack versatility for use with work pieces of different sizes.
The known UV-ozone oxidation systems employ a showerhead type gas diffuser consisting of several small diameter stainless steel tubes attached to a gas inlet manifold which deliver the ozone to the work piece. However, this showerhead type gas diffuser delivers a relatively non-uniform ozone/oxygen flow over the surface of the work piece. Accordingly, the stripping or cleaning process using known UV-ozone systems may not be sufficiently uniform for certain applications where uniform oxidation is critical.
In addition, known UV-ozone oxidation systems employ resistance heaters beneath the sample stage to heat the work piece which is positioned on the sample stage. However, these resistance heaters take a substantial amount of time for heat up and cool down, unnecessarily extending the time required for the stripping or cleaning process.
In addition, in order to achieve a shorter overall process time, it is desirable to have the UV lamp positioned as closely as possible to the work piece on the sample stage. However, because work pieces vary in thickness, sufficient space must be provided in the reaction chamber between the sample stage and the UV lamp to accommodate relatively large work pieces.
Accordingly, it would be desirable to provide an UV-ozone oxidation system with a shortened overall process time and improved uniformity of cleaning or stripping.
The present invention relates to a ultraviolet-ozone oxidation system with an improved uniformity in the delivery of ozone over a work piece to be cleaned or stripped. The present invention also relates to an improved ultraviolet-ozone oxidation system in which the overall process time required for cleaning or stripping a work piece is reduced.
In accordance with one aspect of the present invention, an ultraviolet-ozone oxidation system includes a reaction chamber, an ozone source for delivering ozone to the reaction chamber, a sample stage for supporting a sample in the reaction chamber, a source of ultraviolet light directed at the sample on the sample stage, and a membrane diffiser positioned between the ozone source and the sample stage for uniformly distributing ozone to the sample on the sample stage.
In accordance with an additional aspect of the present invention, an ultraviolet-ozone oxidation system includes a reaction chamber, an ozone source for delivering ozone to the reaction chamber, a source of ultraviolet light, and a movable sample stage for supporting a sample in the reaction chamber. The movable sample stage is movable with respect to the source of ultraviolet light to adjust a distance between the sample supported on the sample stage and the source of ultraviolet light.